The present application relates generally to an improved data processing apparatus and method for cabling multiple enclosures using top-down/bottom-up cabling.
Typically, a storage subsystem comprises multiple enclosures coupled using interconnecting cables for communication capabilities. A typical cabling scheme may involve a controller which couples to a first enclosure, the first enclosure coupling to a second enclosure, the second enclosure coupling to a third enclosure, and so forth. FIG. 1 illustrates one example where enclosures 102 within system 100 have an “A” side and a “B side coupled to controller 104 using a dual-chain scheme. As is illustrated, enclosures 102 above controller 104 are coupled by cables 106 in a different chain from enclosures 102 below controller 104 that are coupled by cables 108. However, for those enclosures 102 coupled by cables 106, if any one enclosure 102 loses power, then the enclosures 102 above and including the enclosure 102 that loses power, become inaccessible. Similarly, for those enclosures 102 coupled by cables 108, if any one enclosure 102 loses power, then the enclosures 102 below and including the enclosure 102 that loses power, become inaccessible.
A common scheme for increasing reliability is to wire one side of an enclosure “top down” and the other side of the enclosure “bottom up.” For example, in FIG. 2, the “A” sides of enclosures 202 in system 200 are coupled by cables 206 to controller 204 in a “bottom-up” scheme and the “B” sides of enclosures 202 are coupled to controller 204 by cables 208 in a “top-down” scheme. The advantage here is that if a whole enclosure 202 loses power, then the left chain of enclosures 202 coupled by cables 208 may still access data above the failure, while the right chain of enclosures coupled by cables 206 may still access data below the failure. If enclosures 202 were coupled in a “top-down” scheme on both chains, then access to the enclosures 202 would only be preserved above the failure.
An enhancement of the cabling scheme of FIG. 2 uses an additional cable to make both sides of the chain “top down” and “bottom up.” For example, in FIG. 3, the “A” sides of enclosures 302 in system 300 are coupled by cables 306 to controller 304 in a “bottom-up” scheme and the “B” sides of enclosures 302 are coupled to controller 304 by cables 308 in a “top-down” scheme. However, an additional cable 310 is added to the “A” side and an additional cable 312 is added to the “B” side to make both sides of the chain “top down” and “bottom up.”
This cabling scheme gives improved reliability but also provides significant performance improvement. Normally, the further an enclosure is from the controller, the lower the average utilization of each link between the enclosures. For example, using the four enclosures depicted in FIG. 3, the connection from controller 304 to the 1st enclosure would be 100% utilized and, on average the link between the 1st and 2nd enclosure would be 75% utilized, the link between the 2nd and 3rd enclosure would be 50% utilized, and the link between the 3rd and 4th enclosure would be 25% utilized. By having controller 304 coupled to both ends and routing requests evenly, “wasted” bandwidth may be reclaimed.
However, feedback from field support teams indicates wiring schemes such as those depicted in FIG. 3 are more prone to being installed incorrectly, especially during the installation of additional enclosures, which requires moving cables as opposed to simply appending to the end of the chain. In the worst case, cabling errors cause invalid network topologies which turn into concurrent service action and further outages for the customer, which increases support costs and decreases customer satisfaction.